Hi, Rural/Urban drivers!
This clogging/blowing-up is quite normal as documented all over.
Eaven vague descriptions get it mostly right.
The consumption stages of wood along the draft passage are
always the same, ash comes always last. (at each draft level)
At each draft level a corresponding volume of char is
glow-activated followed by a passive colder layer.
If the draft is on top, and blows down the ash through narrow
enough passages, that will seldom apply on low draft levels.
Abowe the restriction one can put in extra nozzles
for low draft between the normal nozzles and the restriction.
Always on, or switchable, eaven alternating with the normals.
Low enough, below the restriction, the grate function standard
draft dependent, or jumping vigorously on command.
Peacefully sieving is also offered.
Personal innovation has a large field.